Auto-detect and apply WebKitGTK DMA-BUF workaround on Linux

[kchudy]

Description

Context

On some Linux GPU/compositor combinations (mainly NVIDIA + Wayland), WebKitGTK's default DMA-BUF renderer fails, crashing Defguard Client on launch with:

Gdk-Message: Error 71 (Protocol error) dispatching to Wayland display.

Users currently must manually set WEBKIT_DISABLE_DMABUF_RENDERER=1. Documented by Tauri: https://v2.tauri.app/develop/debug/linux-graphics/

Goal

Detect affected configurations automatically and apply the least invasive fix - without disabling acceleration for unaffected users.

Approach

Do not set the workaround unconditionally for everyone (per Tauri's own guidance - it removes the faster rendering path for users on working setups).

At startup, before webview init:

1. Detect Wayland session (XDG_SESSION_TYPE / WAYLAND_DISPLAY) and NVIDIA driver presence.
2. Skip if the user already set WEBKIT_DISABLE_DMABUF_RENDERER or __NV_DISABLE_EXPLICIT_SYNC manually.
3. If affected: try __NV_DISABLE_EXPLICIT_SYNC=1 first (keeps acceleration). Fall back to WEBKIT_DISABLE_DMABUF_RENDERER=1 only if that's insufficient.
4. Log which decision was made and why.

Alternative/complementary: apply the fix in the package post-install script by patching the .desktop file's Exec line, rather than system-wide.

Acceptance criteria

• App detects Wayland + NVIDIA at startup, before webview init.
• Manually-set env vars are never overridden.
• Tries __NV_DISABLE_EXPLICIT_SYNC=1 before WEBKIT_DISABLE_DMABUF_RENDERER=1.
• No behavior change on unaffected configs (AMD/Intel, X11).
• Decision is logged.
• Troubleshooting docs updated to reflect auto-detection, with manual steps kept as fallback.
• Tested on ≥2 affected setups (e.g. Fedora 44 + KDE + NVIDIA/Wayland) and 1 unaffected setup.

Risks

• NVIDIA driver presence ≠ guaranteed failure (545+ often works fine) - consider checking driver version to avoid unnecessary workarounds.